1. Field of the Invention
The present invention relates to a multiple-power gear drive or transmission including a planetary differential gear drive which encompasses a plurality of gear drive elements such as sun gear, web gear and internal gear whereby a gear drive input shaft is coupled with at least one of these gear drive elements, and a gear output drive shaft with another of these elements. For the control of the direction of rotation and the rotational speed of a third gear drive element, coupled thereto is a positive-displacement machine which is operable in both directions as either a pump or motor, or an electromotor (control power machine) operable in four-quadrant operation, and including a second positive-displacement machine operable as either a pump or motor, or alternatively a second electromotor operable in four-quadrant operation which is energy-transmissively coupled with the control power machine (torque power engine).
2. Discussion of the Prior Art
Multiple-power gear drives of this basic constructional type are known, for example, from the journal "VDI-Richtlinien" (2152), March 1975, FIGS. 3.8.3. and 3.8.4. In these known gear drive representations, the torque power engine, pursuant to its type of construction, is constantly connected with either the gear input drive shaft or the gear output drive shaft. In these gear drives, dependent upon the ratio between the rotational speeds of the gear drive input and gear drive output, a part of the power is transmitted purely mechanically, whereas another part of the power is transmitted through the energy-transmissive coupling of the above-mentioned power machines.
In the construction with constant coupling of the torque power engine to the drive input shaft, in a first operative range of the gear drive in which n.sub.output : n.sub.input &gt;0.5, a part of the power circulates in a negative direction (idle power) from the control power machine to the torque power engine which is connected to the gear drive input shaft. In the other type of construction with the constant connection of the torque power engine to the gear drive output shaft, there takes place a reactive or idle power circulation from the torque power engine to the power control machine with a second operative range, namely, in which n.sub.output : n.sub.input &gt;0.5. These idle power losses adversely influence the efficiency of these known multiple-power gear drives or transmissions.
From German Published Patent Specification No. 15 50 941 there has become known a multiple-power gear drive with two operating ranges and, namely, a first purely hydrostatic range for lower speeds, and a range with power take-off or branching in which the torque power engine is connected with the gear drive input shaft. A shifting from the first operating range to the second operating range takes place in this gear drive at synchronous rotational speeds, however, inasmuch as the hydro-units employed therein are under full load, the reversal in the suction and pressure sides produces strong switching impulses (oil compression) at the instant of the shifting. In addition thereto, the still appreciable component of the hydrostatic power or energy imparts a high noise level to the gear drive.